Gaskets are generally sealing members which are utilized to form a sealing interface between two or more structures. Gaskets are available in range of hardnesses from pliant to rigid. Gaskets made from non-pliant materials, including metals are generally more difficult to make. One of the more difficult gaskets to make is commercially available as GASK-O-SEAL, and is typically used in diesel engines of the type commonly employed in diesel-electric trains.
This gasket is angularly shaped, and has a thick area along its radially inward surface, and a thin area along its radially outward surface. The radially outward surface also contains a series of two types of apertures. One set of apertures is round, and the other have a shape facilitating the placement of inserts. In addition, the radially outward surface has orientation notches to assist in orienting the gasket.
The preferred method of production has been to start with a sheet of cold rolled steel, mask off the areas which are to remain relatively thick, and chemically mill the areas whose thickness are to be reduced. Chemical milling involves the immersion of the part into a bath having an acid or other chemical agent of known strength and reaction rate. The part is typically exposed to the bath for a predetermined amount of time to hopefully result in the removal of a pre-determined amount of the metal, the theory being that the chemical milling bath with cause the removal of the metal evenly. Chemical milling is especially used for very thin parts, since the chemical milling process does not produce harmful forces which might cause thin parts to tear and bend. Chemical milling has been used with gaskets because it was sought to remove material evenly from both sides of the circumferentially outward portion of the gasket.
This method of production has resulted in several production problems. The rejection rate for this method is about fifty percent. Further, chemical milling is not an environmentally sound method. The chemical milling solution is caustic and may not easily be converted to inert compounds after its use. Chemical milling solutions contain heavy metals which are a hazardous waste. Even if the metals can be removed using electrical or chemical methods, these additional process steps drive up the cost, and the chemical milling solution must eventually be disposed.
Further, some caustic chemical milling solutions can invade, attack and change the chemical structure of certain metals. The performance of chemical milling with an improper solution could result in unwanted brittleness, unwanted crystalline defects, or uneven dissolution.
What is needed is a process for making metal and non-pliant gaskets which does not involve chemical milling. The method should result in a minimum amount of metallic scrap, and the scrap which is produced should be amenable to immediate recycling. The needed process should be able to make a product which is consistently of high quality, has zero defects, and which absolutely minimizes the rejection and error rates in manufacturing.